Underwater dredge with separating means



Dec. 15, 1964 J. NOVAK 3,161,438

UNDERWATER DREDGE WITH SEPARATING MEANS Filed July 12, 1961 2 Sheets-Sheet 1 Fig! WW. E 2 m1;

Fig. 2

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INVENTOR M i lion J. Novak ec. 15, 1964 ov 3,161,438

UNDERWATER DREDGE WITH SEPARATING MEANS Filed July 12. 1961 2 Sheets-Sheet 2 3.? Q '63:? is

INVENTOR 7 Milton J. Novok Fig.9 W

United States Patent Ofitice 3,161,438 UNDERWATER DREBGE WITH SEPARATING MEANS Milton .I. Novak, 4418 Normandy, Dallas, Tex. Filed July 12, 1962, Ser. No. 123,596 4 Claims. (it'll. 299-9) This invention relates to mining apparatus, and particularly to mining apparatus for recovering minerals from submerged areas.

One object of this invention is to provide a new and improved mining apparatus for the recovery of valuable minerals from placer deposits in submerged areas.

Another object is to provide a mining apparatus for the recovery of valuable minerals from placer deposits in submerged areas whereby mineral concentrates are recoverable without requiring the surface handling of large quantities of mineral bearing material.

Still another object is to provide an apparatus which will dredge underwater placer deposits containing valuable minerals and is provided with concentrating or separating apparatus for separating the desired concentrates from the gangue material, the'apparatus being operable entirely under water. I

A further object is to provide an underwater mining apparatus for recovering minerals from submerged placer deposits which is operable for mining deposits at shallow or extreme depths.

A still further object is to provide an apparatus for mining submerged placer deposits for recovering valuable minerals therefrom which includes a dredge equipped with a jet nozzle for digging up the sediments by means of water under pressure delivered through the jet, means for receiving the deposits which are dug up by the jet nozzle, means for separating the heavy minerals from the dredged up deposits, means for concentrating the heavy minerals, and means for recovering the concentrates from the apparatus while it is submerged.

A still further object is to provide an underwater mining device for dredging and recovering valuable minerals from submerged placer deposits which comprises a tubular structure equipped with means providing a venturitype action for dredging up the submerged deposits and drawing the dredged-up deposits into the tubular structure, and separating and concentrating means within the tubular structure for separating out and concentrating the heavier minerals from the dredged-up materials.

Additional objects and advantages of the invention will be readily apparent from the reading of the following description of a device constructed in accordance with the invention, and with reference to the accompanying drawings thereof; wherein:

FIGURE 1 is a schematic view of the dredging and mining device which embodies the apparatus of this invention, shown lowered over the side of a dredging vessel in a position for dredging and mining operations;

FIGURE 2 is a top plan view of the dredging and mining device;

FIGURE 3 is a side view of the dredging and mining device in FIGURE 2;

FIGURE 4 is a rear view of the dredging and mining device in FIGURE 2;

FIGURE 5 is a fragmentary sectional view of the inlet or intake portion of the device;

FIGURE 6 is a fragmentary sectional view of the outlet end portion of the device;

FIGURE 7 is a sectional view taken along the line '77 of FIGURE 5;

FIGURE 8 is a sectional view taken along the line 88 of FIGURE 6; and,

FIGURE 9 is a side view of the liquid pulsator included in the device, part of which is broken away and shown in section.

Referring now particularly to the drawings, the apparatus of this invention comprises a dredge 10 which may be lowered over the side of a dredging vessel 11. The dredge is lowered adjacent the sea bottom on suspension cables 12 and 13 by a pair of constant lift spring-type cranes 14 and 15, respectively, and is oriented to a position where it is adapted to dredge placer deposits, such as the terrace type placer deposits 16 which overlie the bedrock 17. The tailings or gangue 18 which are separated by the apparatus are discharged under water by the dredge and accumulate on the bedrock behind the dredge. During a mining operation, the dredging vessel may be provided with a bow and stern anchors 19, if desired.

The dredge Ill comprises a tubular housing structure 20 having a downwardly curved snout or mouth portion 21 and an expanding section 22 which expands gradually as it extends from the throat end of the curved mouth portion 21 to the outlet end 23 of the housing. The sides 24 and 25 of the dredge are integrally formed with the roof or top 26 and are disposed parallel with one another throughout the length of the dredge. In use, the dredge is normally oriented with the inlet 27 at the mouth of the dredge opening downwardly and the top of the dredge disposed substantially horizontally. A curved plate 28 forms the door of the mouth, the passageway of which is uniform in dimension from its inlet end to the point at which it communicates with the passage provided by the expanding section 22.

The expanding section 22 of the dredge includes an upper chamber or passage 30 and a pair of lower chambers 31 and 32 therebelow, the separation of the upper chamber from the lower chambers being effected by a separating screen 33 of specific and predetermined aperture size. The screen 33 slopes downwardly from the throat of the curved section 21 towards the outlet end of the dredge and by its divergence from the roof of the dredge provides a gradual expansion of the upper chamber 30. The screen, which may be provided with a peripheral frame, is attached to the inner end of the curved plate 28 along its sides to the dredge sides 24 and 25 by any suitable means, such as welding. At its lower after end the screen is attached to a tail plate36.

The lower chambers 31 and 32 are defined by a pair of channel troughs 41 and 42, respectively, of semicircular cross section and disposed in side by side relation to one another with their inner adjacent side edges abutting the lower surface of the separating screen. The outer side edges of the troughs are secured to adjacent sides of the housing structure by any suitable means, as by welding. The rear ends of the chambers 31 and 32 communicate with a jigging chamber 44 which extends from the chambers 31 and 32 to the outlet end of the dredge. A plate 45 welded to the lower curved surfaces of the channel troughs forms a portion of the bottom of the housing structure and with the walls of the channel troughs defines a chamber 46 located between the chambers 31 and 32 and in communication therewith by means of a number of ports 47 which are formed in the walls of the channel troughs directly above the plate 45. The forward ends of the lower chambers 31, 32 and 46 are closed by a transverse wall 48.

At its forward end adjacent the inlet 27 the dredge is equipped with a jet nozzle 50, which is directed upwardly and inwardly towards the center of the throat of the curved section of the dredge. The outlet 51 of the nozzle jet may extend substantially the width of the throat of alternatively a plurality 'of transversely spaced outlets may be provided.

A centrifugal pump P located in the dredging vessel 11 supplies water at a relatively high pressure to the noz- Patented Dec. 15, 1964 p 3 'zle50 through a'flexible pipe 54 which connects the outlet of the pump with a distribution mainfold 55 located atop the housing structure. The water is delivered to the nozzle from the manifold by a delivery conduit 56 also located atop the housing structure 24). The nozzle "55 causes movement of water through the-chamber 30 at a predetermined velocity. The venturi action of the-water whichis forced-through the nozzle 50 produces a low pressure area'around the jet which'tends to draw additional fluid into the active area through the-inlet 27 of the dredge. The drawing action of the water expelled from the jet, characteristically is at right angles to the direction of When the drawing action occurs near a water-sediment interface, as when the dredge is operationally positioned above the placer deposits 16 shown in FIGURE 1, the water drawn into the inlet 27 will erode and transport sedimentary particles of the placer deposits when certain critical velocities are reached. The curved plate 28 in the mouth of the dredge is so disposed relative to 'thenozzle '50 as to intercept and direct upwardly the eddy action produced at the underside of the jet whereby all of the dredged material entering the dredge is caused to traverse the turbulence in the throat of the dredge produced by the jet, thus inducing a further break-up of the sedimentary particles.

An additional jet nozzle '60 is also provided adjacent the inlet port at the mouth of the dredge but is directed downwardly therefrom. Thisjet, which is also connected to the conduit 56 to receive water under pressure from the centrifugal pump in the dredging vessel, is used primarily for digging the placer sediments. Since the very heavy minerals, particularlythe larger fragments of the naturally occurring metals are ditiicult to remove from an irregu- 'lar bedrock surface by laterally moving Water such as produced by the Venturi action of the dredge, the.digging nozzle 60 produces a jet of water directed vangularly at such deposits and causes them to be displaced from the bedrock surface so that they may more easily be drawn into the inlet .of the dredge. As illustrated in FIGURE 5, the jet of water from the digging nozzle is directed at approximately a 45 degree angle to the sediment surface whenin operationso that thejet stream from the nozzle 60 is refiectedot the dredge mouth along with-the sediment contained .in suspension which have been eroded from the placer deposits. It is thus apparent that the energy of the jet stream from the nozzle 60 is transferred in a preferred direction, namely, inthe direction of the inlet 27 of the tubular dredge.

While the lower jet nozzle -60 is used primarily for digging, its use is optional and its exact location, size, and orientation are entirely arbitrary. However, the particular arrangement of the jets as describedabove is generally most etfective'to produce the five to the percent solids-to-liquid ratio which is most easily treated for heavy mineral recovery in the dredge. The movement of water through the :dredge as produced primarily by the jet nozzle 50is predetermined by the design of the jet nozzle and the supplied fluid pressure to effect a velocity which will permit the recovery equipment located in the rear portion of the dredge to function efficiently. For reducing clayseams and-(chunks which are otherwise too large to pass the .dredgemouth, supplemental hydraulic energy or mechanical devices may be provided, asdesired.

It will be noted that the-construction of the tubular dredge through which the influent water and sediments are drawn provides for an upper water course in the chamber above the separating screen and lower water courses inthe chambers'below the screen. In the operation of the mining device, "the influent water and sediment which pass through the throat of the dredge into the expanding section thereof are subjected to a deceleration because of the continuously expanding upper chamber 30 of the dredge so that ;the:particles carried in suspension, by the influent water, particularly the denser mineral particles, are allowed to settle on the screen 33. The smaller particles, however, pass through the screen and enter the lower chambers of the dredge where they are subjected to a further separating process. The larger particles, generally the .gangue minerals, which are of a size too large to pass through the separating screen either settle on the screen or are bounced therealong to the rear portion of the dredge where they are passed through the outlet port 61 at theoutlet end of the dredge. This initial screening provided by the separating screen eliminates approximately ninety percent of the gangue 'minerals from the dredged-up materials when the separating screen apertures are of correct size and'the fluid movement of correct speed. Excessive speed of the water through the passage or chamber 30 reduces recovery of minerals from the dredge-up materials by not allowing sufiicient time for the bulk of the particles to settle to the screen and also by generating eddy currents on the screen surface which causes the recirculation of particlesto prevent their settling to the screen. Normally in order to erode, move, and lift the coarser sediments, such as pebbles and gravel, the jet velocities may exceed one to three meters per second and during the settling jprocess, velocities of water through the chamber '30 'must range between 0.3 and 0.6 meter per second.

In the usual operating technique employed in the miningprocess, it is customary to use a separating screen provided with apertures which are just smaller than the average size of the gangue minerals or which are as large as the coarsest monomineralic heavy mineral grains. Approximate knowledge of the average grain size passing throughthe dredge can generally be maintained by .close watch of the .concentrates which are recovered. Sands and gravels canbe worked on separating screens in the sixty to five mesh sizes, respectively. Screens finer than one hundredmesh would handle excessive quantities of the difiicult to settle silt sized particles. However, should deposits of this nature prove to be of interest, the dredge would require the additional design features of larger screen surfaces and provision for slower fluid velocities over the screen surface.

In the usual orientation of the dredge during mining operations, the slight slope of the screen 33 relative to the top of the dredge adds a gravitational component to the horizontal forces acting on the grains or particles which tend to prevent screen loading or blinding. In addition, a pulsator'65 located .atop the dredge is adapted to supply pressure pulses to the water flowing in the lower water course of the dredge, which pulses are-transmitted upwardly through the screen 33 to induce the further settling of the heavier specific gravity particles adjacent'the screen surface. The apertures 47 are positioned and of such size as to allow the pulsating, upwardly transmitted water from the lower water courses to have a relatively greater effect or flow at the dredging or snout end. This flow rate then through the use of smaller or more widely spaced apertures is gradually lessened towards the discharge end of the dredge.

The pulsator 65, which may be of any desired design is connected to the pressure manifold 55 by -a conduit 66,'receives approximately 25 percentofthe water which is delivered to the manifold through the flexible pipe 54, the remaining 75 percent being delivered to the nozzles in front of the dredge. The pulsator generates a rhythmic surging or pulsing action which is transmitted to the lower water courses of the dredge by means ofthe conduit 67 which communicates the outlet of the pulsator with'the lower chambers of the dredge. The outlet end of the conduit 67 is connected through a suitable aperture in the transverse vertical jig plate 68 at the end of the housing structure.

On passing through the separating screen 33,'the product, a low grade concentrate, accumulates in the lower chambers .31 and 32 and gradually moves along the bottom of the troughs into the chamber 44 and onto a fine mesh screen 80, shown in FIGURE 6, which is attached at one end to the bottom of the troughs and at the other end to a bracket 81 which extends inwardly from the jig plate 68. A plate 82, preferably perforated, is disposed below the fine screen 80 and above the jig pan or bottom 83 of the chamber 44. It will be noted that the pressure pulses delivered to the water in the chamber 44 are transmitted upwardly through the fine screen 80, thereby agitating the particles above the fine screen to induce the gravitation of the denser particles towards the screen. The end result is Stratification of the min erals according to their specific gravities with a small percentage of the very fine particles passing through the fine screen into the hutch 44a formed between the screen and the plate 82. When there is a sufficient accumulation of gangue material on the jig screen, a pair of floats 85 are moved upwardly thereby to open the valves 85 which control the flow of materials through the discard pipes 87 which extend through the bracket plate 81 and M the transverse rear wall or jig plate 68 of the dredge. It is therefore apparent that when a sufiicient quantity of material accumulates on the jig screen the floats will open the valves 86 to permit the discharge of the lighter sands or gangue material from the rear of the dredge. The heavier concentrates which accumulate onthe fine jig screen move slowly into the inclined pipes 88 and 89 which are disposed at the lower rear end of the jig screen 80 in a position to receive the concentrates which are moved toward them. The outlets of the pipes 88 and 89 communicate with a delivery pipe 90 which extends transversely across the lower rear end of the housing structure to form the juncture of the jig plate 68 and the jig pan 83. The delivery pipe 90 is provided with a longitudinal slot 91 through which the concentrates delivered from the pipes are receivable therein. Any concentrates falling through the apertures of the plate 32 and on the bottom 83, also tend to move down the rearwardly and downwardly inclined plate 83 to the longitudinal slot 91 of the delivery pipe to be transported thereby to the dredging vessel. The pipe 00 has a portion 92 which extends exteriorly of the housing structure along the side thereof to the top of the dredge where it is connected in fluid communication with a flexible recovery pipe 93 which leads to the dredging vessel. A centrifugal pump 94 in the dredging vessel is employed to recover the concentrate through the flexible pipe 93. Other lifting devices, of course, may be employed for this purpose. The flexible pipes 54 and 93'are supported by lift cranes 95 and 06 similar to the cranes which support the cables 12 and 13. Any suitable connection between the pumps and flexible pipes 54 and 93 may be employed. The flexible pipes, if desired, may be reeled on a drum and a swivel to axle to pipe type of connection be employed.

A pulsator of a type suitable for use with the dredge is disclosed in FIGURE 9. The pulsator is comprised of a liquid chamber A and an air chamber B which are separated by a flexible diaphragm 100. The liquid chamber B is defined by a cylindrical member 101 and communicates with the manifold 55 by means of the conduit 66. The diaphragm 100 is clamped by bolts 102 disposed through the aligned apertures in the diaphragm and the peripheral flanges 103 and 104 which are provided respectively on the upper end of the cylinder 101 and the lower end of the inverted cup-like member 105' which defines the air chamber B. The pulsator outlet conduit 67 which communicates the pulsator with the lower chambers of the dredge extends through the wall of the cylinder 101 and is closed at its open upper end by a valve element 106 located centrally on the diaphragm. The diaphragm and valve element are normally biased downwardly to close the conduit 67 by means of a coil spring 107 disposed about the tubular guide 108 which extends downwardly from the cup-like member toward the diaphragm. One end of the spring 107 engages the inner surface of the cover or cup-like member 105 and its other lower end engages an annular disc 109 disposed flat against the upper side of the diaphragm. The disc 109 and valve element 106 are clamped to the diaphragm by a bolt 110 which extends through the tubular guide and aligned apertures in the disc, diaphragm, and valve element, respectively. A clamping nut 111 threaded on the lower end of the bolt clamps the disc, diaphragm and valve element against a downwardly facing shoulder 112 provided on the bolt.

In operation, water under pressure from the manifold enters the liquid chamber P and forces the diaphragm upwardly against the action of the spring 107 to open the conduit 67. Water escaping from the liquid chamber B and entering the conduit 67 thus reduces the pres sure in the liquid chamber to permit the valve to close in response to the action of the spring 107. Once the valve closes, the pressure in the liquid chamber B again rises to open the valve. In this manner a pulsating flow of water is caused to move into the housing structure through the conduit 67 into the lower chamber of the housing structure.

Although the embodiment of the dredging apparatus disclosed herein includes a dredge which is suspended from suspension cables 12 and 13- and raised or lowered by the cranes 15 and 14, it is entirely possible to suspend the dredge by means of the flexible conduits 54 and 93 which in addition to performing their respective functions of delivering water to the jet nozzles and re covering the concentrates would also serve to suspend the dredge. The dredging and mining device could then be lowered or raised by the cranes which control the movements of the flexible pipes, thus simplifying the construction and operation of the device.

It will thus be seen that a new and improved form of mining apparatus is disclosed herein which-includes means for dredging placer sediments along a marine bottom and mineral separating apparatus incorporated therewith, which mining apparatus is operable from a remote point such as a dredging vessel, and which is entirely operable while submerged.

It will further be seen that a deep sea dredging and mining apparatus is disclosed herein which includes a tubular dredge adapted to operate on the Venturi principle for drawing sediments from placer deposits on a sea bottom into the dredge whereby the sediments are adapted to be broken up by hydraulic action and subjected to treatment by mineral separating apparatus incorporated within the dredge whereby valuable minerals may be recovered from the sediments.

It will further be seen that a new and improved type of underwater dredging and mining apparatus is disclosed herein which includes a tubular dredge equipped with means adapted to produce jet streams of water for breaking up placer sediments along a marine bottom and drawing influent water and sediment into the dredge and separating apparatus for separating heavy valuable minerals from such sediments, which valuable minerals are recoverable from the apparatus by suitable pump means.

The foregoing description of the invention is explanatory only, and changes in the details of the method described and construction illustrated may be made by those skilled in the art, within the scope of the appended claims, without departing from the spirit of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. A placer mining device for mining submerged placer deposits comprising: an elongate tubular housing positionable adjacent and above a submerged placer deposit having a passageway extending longitudinally therethrough; said tubular housing having an inlet end and an outlet end, the portion of said passageway adjacent said inlet end being of substantially uniform cross sec- 7 tion, :the portion of saidgpassageway extending from said portion of uniform cross section to the outlet end of said housingbeing ofrincreasingcross-section toward said outlet end; a .first jet'nozzle mounted .on said housing adjacent said inlet .end, said :jetinozzle beingoriented to deliver a stream of .Water idownwardlyifrom said housing against :said .placer deposits when .COIlIlfiCiBdztO a supply of water under pressure; a .second jet nozzle adjacent the inlet endof said :tubular housing, said second noz zle being .oriented to deliver a stream of water under pressure into the portion .of uniform cross-section of said passageway when said second ;jet 'nozzle is .eonnected to a supplyof water under pressure, whereupon materials excavated by said rfirst .-jet nozzle are caused to enter the inlet end of said tubular housing and are forced through .theipassageway thereof-by the-stream delivered by said second jet nozzle; means for delivering water under pressure .to said :jet tnozzle; :screen means in said housing between said;portion of said :passageway of uniform cross-section area and the outlet end for separating the excavated :material into a first portiont-hav- .ing only particles which are smaller than :a predetermined size and a second portion having only particles which are greater than said predetermined size, said screen means forming the lower boundary of-said;-portion of said passageway extending :from saidportion of uniform cross-section to the outlet end; means within said tubular housing .adjacentzthe outlet end thereof ,for stratifying the portion :of said smaller sized particles in accordance with their specific gravities; means for ejecting the strata of lighter specific gravity particles from said tubular housing; :and :means for recovering from said housing the lower strata of particles of heavier specific gravity.

2. A mining apparatus for mining submerged placer deposits comprising: xaitu'bular housing positionable adjacent and immediatelyabove a submergedplacerdeposit, said housing having a-longitudinal passageway extending therethrough from .an inlettend to ;an-1outlet .end :thereof, said passageway having :a portion :of runiform-crosssection extending from the inlet :end of .said :housing :toward the outlet end thereof, said passageway :having .a portion of expanding cross-section extending from said portion of uniformcross-section to :the routlet :end .o'f1said housing; means mounted on said .housing adjacent the inlet end for excavating placer tdeposits; first means mounted on said housinganfl locatediadjacent the inlet end of said housing for :delivering a iflllid jet stream through the passagewayiof saidhousing in :a .direction away from said inlet end twherehy material excavated '18 by said excavating .means and entering the inlet end of said tubular housing is forced :through said passageway by said first means; a first screen extending from said .outlet end of said housing upwardly .at a slight angle from the .horizontal to the portion .of the passageway of uniform cross-section, said housing having a lower chamberbelowsaid screen, said screen forming the lower boundary of said portionof said passageway of expanding cross-section; means .of said tubular housing defining the upper boundary of said portion of said flow passage of expanding cross1section extending substantially horizontally whereby .the velocity .of flow of fluids through said portion of said passage .of expanding cross-section gradually decreases as the fluid moves toward the outlet end of said housing through said portion of said passageway of expanding cross-section and the .excavated material which is moved through said passageway is caused .to settleupon said screen with the particles smaller than the apertures .of said screen passing through said screen into said lower chamber and the particles larger than the apertures of said screen being discharged from said passageway at the outlet end of said housing; means in .the lower chamber .of .said tubular housing for separating saidsmallerparticles in accordance with their specific gravity; and 111163.115 insaidftubular housing for recovering the particles of heavierspecific gravity.

3. The mining apparatus of claim 2 wherein said means in the lower chamber of said tubular housing for separating .said smaller particles .in accordance with their specific gravity includes asecond screen and a second means for introducing .a .pulsating flow of fluid into said lower chamber for flow upwardly through said second screen and said first screen.

4. The mining apparatus of claim 3, .and means in said housingbelow said first screen for causing the fluid introduced into said housing .by said second means to flow upwardly throughsaid first screen and for causing its rate of upward flow through portions of said first screen more-remote from said .outlet end to be greater than its rate of upward flow through portions of said first screenless remote from said outlet end.

References-Cited in the 'file of this patent UNLTED STATES PATENTS 281,415 Stone July 17, 1883 594,041 Strong Nov. 23, 1897 1,230,274 Caldwell June 19, 1917 2,055,161 Vissac Sept. 22, 1936 2';073,122 'Silke Mar. 9, 1937 UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No 7 5 161 438 December 15 1964 v Milton Jo N'ovak It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line 68 for throat of" read throat or column 4 line 23 for "may'' read must Signed and sealed this 18th day of May 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PLACER MINING DEVICE FOR MINING SUBMERGED PLACER DEPOSITS COMPRISING: AN ELONGATE TUBULAR HOUSING POSITIONABLE ADJACENT AND ABOVE A SUBMERGED PLACER DEPOSIT HAVING A PASSAGEWAY EXTENDING LONGITUDINALLY THERETHROUGH; SAID TUBULAR HOUSING HAVING AN INLET END AND AN OUTLET END, THE PORTION OF SAID PASSAGEWAY ADJACENT SAID INLET END BEING OF SUBSTANTIALLY UNIFORM CROSS SECTION,THE PORTION OF SAID PASSAGEWAY EXTENDING FROM SAID PORTION OF UNIFORM CROSS SECTION TO THE OUTLET END OF SAID HOUSING BEING OF INCREASING CROSS-SECTION TOWARD SAID OUTLET END; A FIRST JET NOZZLE MOUNTED ON SAID HOUSING ADJACENT SAID INLET END, SAID JET NOZZLE BEING ORIENTED TO DELIVER A STREAM OF WATER DOWNWARDLY FROM SAID HOUSING AGAINST SAID PLACER DEPOSITS WHEN CONNECTED TO A SUPPLY OF WATER UNDER PRESSURE; A SECOND JET NOZZLE ADJACENT THE INLET END OF SAID TUBULAR HOUSING, SAID SECOND NOZZLE BEING ORIENTED TO DELIVER A STREAM OF WATER UNDER PRESSURE INTO THE PORTION OF UNIFORM CROSS-SECTION OF SAID PASSAGEWAY WHEN SAID SECOND JET NOZZLE IS CONNECTED TO A SUPPLY OF WATER UNDER PRESSURE, WHEREUPON MATERIALS EXCAVATED BY SAID FIRST JET NOZZLE ARE CAUSED TO ENTER THE INLET END OF SAID TUBULAR HOUSING AND ARE FORCED THROUGH THE PASSAGEWAY THEREOF BY THE STREAM DELIVERED BY SAID SECOND JET NOZZLE; MEANS FOR DELIVERING WATER UNDER PRESSURE TO SAID JET NOZZLE; SCREEN MEANS IN SAID HOUSING BETWEEN SAID PORTION OF SAID PASSAGEWAY OF UNIFORM CROSS-SECTION AREA AND THE OUTLET END FOR SEPARATING THE EXCAVATED MATERIAL INTO A FIRST PORTION HAVING ONLY PARTICLES WHICH ARE SMALLER THAN A PREDETERMINED SIZE AND A SECOND PORTION HAVING ONLY PARTICLES WHICH ARE GREATER THAN SAID PREDETERMINED SIZE, SAID SCREEN MEANS FORMING THE LOWER BOUNDARY OF SAID PORTION OF SAID PASSAGEWAY EXTENDING FROM SAID PORTION OF UNIFORM CROSS-SECTION TO THE OUTLET END; MEANS WITHIN SAID TUBULAR HOUSING ADJACENT THE OUTLET END THEREOF FOR STRATIFYING THE PORTION OF SAID SMALLER SIZED PARTICLES IN ACCORDANCE WITH THEIR SPECIFIC GRAVITIES; MEANS FOR EJECTING THE STRATA OF LIGHTER SPECIFIC GRAVITY PARTICLES FROM SAID TUBULAR HOUSING; AND MEANS FOR RECOVERING FROM SAID HOUSING THE LOWER STRATA OF PARTICLES OF HEAVIER SPECIFIC GRAVITY. 